Sexual impotence is a common male disorder affecting 10-12 million men) that can have great significance for health and health-care expenditures. Despite its prevalence, costs, and implications for quality of life impotence remains poorly understood in relation to the endocrine function, medication usage, lifestyles, anthropometrics and behavior (including alcohol consumption, smoking, and nutrition) in the susceptible populations of middle-aged and older men. No definitive population-based study of impotence has been conducted since, despite major changes since that time in social attitudes, possible new causes such as chemical hazards and clinical advances addressing impotence as a vascular disorder. An NIH Consensus Development Conference (1992) lamented the absence of epidemiologic studies of impotence and concluded there is an urgent need for work in this area. There are no normative data on male sexual functioning. The Massachusetts Male Aging Study (MMAS) in its baseline phase (t1, 1986- 90) assembled the largest population-based, cross-sectional database on male endocrine function, health status, sexual functioning, and psychosocial correlates available worldwide. Unique aspects of MMAS include * a random sample of free-living, apparently healthy men aged 38- 70; * a high yield (1709) of complete responses, permitting precise estimation of key parameters while controlling for confounders through subgroup analyses * a wide range of measures including sexual behavior, health status, medication usage, and physiologic, anthropometric, sociodemographic, and psychosocial variables comprehensive hormone, nutritional and lipid profiles; * an in-home protocol, including early- morning blood sampling and interviewer-administered instruments; * quality-control activities and validation substudies ensuring the high quality of the data. The proposed longitudinal follow-up is designed to examine two principal endpoints- impotence and hormone profiles - in the same MMAS subjects six years after the baseline study (t2, 1993-97) to address :(1) What was the incidence of impotence (new cases per year per 1000 men between t1 and t2? What changes occurred in the hormone profiles? (2) What was the relationship between the principal endpoints and the various classes of intervening variables, namely, sociodemographics; health status and medical care;psychosocial factors; and behavioral factors? Did the-cross- sectional relationship differ between t1 and t2? Did changes within subject in the intervening variables correlate with changes in hormones and impotence? (3) What is the prevalence of impotence (cases per 1000 men) in a normal population of free-living, apparently healthy men? The methods for data collection will be identical to those of the baseline MMAS. Trained technicians will recontact and re visit-the original MMAS sample (75 % are expected to be still available). The research proposed will provide the most comprehensive picture to date of impotence, hormones, and their physiological, psychosocial, and behavioral correlates in normal men.